Process comprising washing rayon in cake form with an aqueous solution of a lower aliphatic aldehyde



May 3, 1960 A. M. SPINING. JR 2,935,373

PROCESS COMPRISING WASHING RAYON IN CAKE FORM WITH AN AQUEOUS SOLUTION OF A LOWER ALIPI-IATIC ALDEHYDE Filed March 27, 19s? RAYON COLLECTED III CAKE FORII PURIFICATION a ALDEIIYDE WASH I,

DRYING INVENTOR ARTHUR MILTON SPINING, JR.

BY 8%TTORNEY United States Patent PROCESS COMPRISING WASHING RAYON IN CAKE FORM WITH AN AQUEOUS SOLUTION OF A LOWER ALIPHATIC ALDEHYDE Arthur Milton Spining, Jr., Nashville, Tenn., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application March 27, 1957, Serial No. 648,790

8 Claims. (Cl. 18-54) This invention relates to the treatment of viscose rayon in cake form. More particularly, itrelates to a means for reducing yellow shoulder stains which are frequently found on such cakes after drying.

Acid rayon cakes produced by the viscose process are prepared by spinning viscose into an acid coagulating and regenerating bath and then collecting the filaments in the form of cakes in spinning buckets. The bucket cakes are then washed with soft water, desulfured and bleached according to conventional procedures. Such conventional processes are disclosed in U.S.P. 2,060,097, U.S.P. 1,931,266, and U.S.P. 2,116,210. If a finished yarn is desired, the bucket cake, after bleaching, is showered with a finish solution. The cakes are then wrung centrifugally in buckets rotating at approximately 3800 revolutions per minute for about 1 minute to remove free water and associated dissolved materials. sleeves are then placed over the cakes leaving only the two ends and inside exposed. The cakes are placed in a drier which contains several zones of decreasing relative humidity. The drying temperature is usually in the Snugly fitting rubber J range of 130-160" F. The drying cycles are so regulated k that the cakes emerging from the driers have average moisture contents in the range of 3.5-4.0%. After removal of the rubber sleeves, the cakes are held in a controlled humidity area until theyhave regained moisture to an average of about 9.5-10.5 total moisture. They are then ready for winding, reeling, beaming, or other textile operations.

In spite of all precautions, a large number of rejects were made because of yellow shoulder stains. In order to ,have yarn which is commercially acceptable, it must be of uniform whiteness and any stains of this type are detrimental to the product. The presence of yellow stains became a problem of considerable magnitude as the size of cakes was increased from 1 to 2 poundsto take advantage of reduced handling costs in the process. The conversion of the spinning machines to the production of larger cakes, therefore, was not possible because of the high incidence and extreme intensity of yellow shoulder stains on 2-pound cakes.

The stains were at first considered to be the result of inadequate purification, or possibly contaminants from some of the purification showers. Accordingly, the first attempts to find a way of eliminating stains was by changes in the purification process. Treatment times for the various showers described above were increased by as much as 50%, both individually and collectively, but there was no noticeable improvement in the condition of the cakes as regards staining. The first shower was modified to be more alkaline, so that it had a pH of 8.5-9.0 instead of 7.5-8.0. The second, or desulfuring shower, was operated in such a way as to have maximum freedom from impurities and also with completely fresh solution. None of these procedures gave any significant improvement in the cakes.

Tests were also conducted with the finish shower. It was modified by eliminating, first the soluble starch and 2,935,373 Patented May 3, 1960.

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then the organic acid, but severe staining of the cakes continued. The condition was not improved by eliminating the finish shower altogether.

It was thought that more complete removal of solution before drying might help. However, neither high speed centrifuging at approximately 8,000 revolutions per minute, nor doubling the time of centrifuging gave any appreciable reduction in stains. The cakes are dried while in tight fitting rubber sleeves in order to minimize dyeing non-uniformities. This method of drying causes a wicking of water and dissolved substances from within the cake to the exposed ends or shoulders of the cakes. in an attempt to make the soluble substances wick onto another surface, some cakes were wrapped in canton fiannel before drying. However, these cakes were also badly stained. a

It is an object of this invention to provide a method for purifying and finishing viscose process regenerated cellulose so that staining is avoided. Another object is to provide a solution suitable for use in the above process which will substantially eliminate staining. Other objects of the invention will become apparent from the following disclosure and claims.

In accordance with this invention, it has been found that cakes which are practically free from stains are obtained are obtained by washing the cakes with an aqueous solution of a lower aliphatic aldehyde, preferably form; aldehyde, prior to the drying of the cakes. Repeated tests have confirmed the first results that concentrations of -1000 parts per million are effective. Preferably, the concentration of the aldehyde in the solution is from 200-500 parts per million. When formaldehyde is used, the commercial solution (37%) may be diluted and used in this form or it may be added directly to the finish solution or the components which are used to prepare the finish solution. Acctaldehyde and other lower aliphatic aldehydes may be used in a similar way.

Yarns treated with finish showers containing form.- aldehyde were evaluated and found to be normal with respect to dyeing, physical properties (before and after accelerated aging), hand and frictional properties. Knit fabric prepared with formaldehyde-treated yarn was used to determine any elfect on human skin. Tests on 204 individuals found no primary irritations or allegric sensitization in the subjects tested.

It is customary to apply a finish solution to rayon cakes for use in the textile trade and the most convenient meth- 0d .of applying the aldehyde in this situation is to comblue it with the finish solution. However, if cakes are produced for any reason without the application of a finish the aldehyde may be applied to the cakes by sub.- stituting a water solution of aldehyde for the finish solution with the concentration of aldehyde being the same as indicated for the finish solution. The temperature of the solution is not critical and. may be selected as convenient.

- Although the aldehyde may be'applied in combination with any of the conventional, aqueous finish solutions known to the art, the preferred finish contains 0.02% to 0.15% soluble starch, 0.1% to 1.0% dispersed mineral oil (liquid petrolatum) and 0.02% to 0.05% of a weak hydroxyl-bearing organic acid such as citric, tartaric, acetic, propionic, lactic, etc.

Figure 1 is a schematic illustration of the process of the present invention.

The effectiveness in reducing the incidence and intensity of yellow shoulder stains is shown by the following examples, which illustrate preferred embodiments of the invention but are not to be construed as limitative.

Example 1 Purified viscose rayon cakes, which had been spun and purified in the conventional manner by extruding viscose into an acid sulfate spinning bath, collecting the yarn in a centrifugal spinning bucket and thereafter washing, desulfuring and bleaching the cakes, were showered for 4 hours with a finish solution at a temperature of 50 C. The finish solution contained 0.1% soluble starch (as defined in the Merck Index, 6th Edition, page 903), 0.05% citric acid, and 0.2% light mineral oil (liquid petrolatum) dispersed in the solution. The cakes were then centrifuged at 3800 r.p.m. for 1 minute, placed in snugly fitting rubber sleeves leaving only the ends and inside exposed, and dried at 130160 F. to an average moisture content of 3.5 to 4.0% and a weight of 1.7 pounds. These cakes constituted a control. The procedure was then modified by adding 500 parts per million of formaldehyde to the finish shower solution for a second group of cakes which were the test cakes. Except for the formaldehyde, these test cakes received exactly the same treatment as the control cakes. The marked improvement in reducing stains is shown by the following report on inspection.

Periodic analysis of the finish solution for free formaldehyde, indicated no appreciable reaction of the formaldehyde with the ingredients of the finish solution.

Control No HCHO in Finish Shower Test 500 ppm. ECHO in Finish Shower No. Percent No. Percent Cakes tree of stains 118 30 519 82 Cakes with slight stains 79 20 85 14 Cakes with stains-reject intensity... 193 50 27 4 Total number of cakes inspected. 390 631 Example 2 Control N o HCHO in Finish Shower Test 200 ppm. HCHO in Finish Shower Control No HCHO 1n Finish Shower No. Percent No. Percent No. Percent Cakes free of stains 0 291 98 0 0 Cakes with slight stains. 247 S1 2 241 80 Cakes with stains-reject intensity 57 19 0 0 59 20 Total number of cakes insp 304 296 300 Example 3 The'test of Example 2 was repeated using acetaldehyde instead of formaldehyde. A similar improvement in the test cakes over the control cakes was obtained.

Many modifications will be apparent to those skilled in the art from the reading of the above without a departure from the inventive concept.

This application is a continuation-in-part of US. application Serial No. 399,581, filed December 21, 1953, now abandoned.

What is claimed is:

1. In a process for producing viscose rayon by the successive steps of spinning a viscose solution, coagulating and regenerating the spun filaments in acid solution, collecting the regenerated filaments in the form of a cake, purifying the filaments in cake form and drying the cake, the improvement which comprises washing the cake with an aqueous solution of a lower aliphatic aldehyde prior to the drying of the cake.

2. The process of claim 1 wherein the aqueous solution of the lower aliphatic aldehyde contains from 50 to 1000 parts per million of the aldehyde.

3. The process of claim 1 wherein the lower aliphatic aldehyde is formaldehyde.

4. The process of claim 1 wherein the lower aliphatic aldehyde is acetaldehyde.

5. In a process for producing viscose rayon by the successive steps of spinning a viscose solution, coagulating and regenerating the spun filaments in acid solution, collecting the regenerated filaments in the form of a cake, washing the cake to remove acid, washing the cake with a desulfuring solution, washing the cake to remove desulfuring solution and drying the cake, the improvement which comprises washing the desulfurized cake for a period of 2 /2 to 6 hours with an aqueous finish solution containing from 50 to 1000 parts per million of an aldehyde from the group consisting of formaldehyde and acetaldehyde at a temperature of 40 C. to C. prior to drying the cake.

6. A process as defined in claim 5 in which said aqueous finish solution contains formaldehyde.

7. A process as defined in claim 5 in which said aqueous finish solution contains acetaldehyde.

8. A process as defined in claim 5 in which said aqueous finish solution contains from 200 to 500 parts per million of the aldehyde.

References Cited in the file of this patent UNITED STATES PATENTS 1,931,266 Parker Oct. 17, 1933 2,060,097 McKee et al. Nov. 10, 1936 2,116,210 McKee May 3, 1938 2,787,517 Lekkerkerker Apr. 2, 1957 OTHER REFERENCES Textile Research Journal, November 1948, pp. 643- 649. 

1. IN A PROCESS FOR PRODUCING VISCOSE RAYON BY THE SUCCESSIVE STEPS OF SPINNING A VISCOSE SOLUTION, COAGULATING AND REGENERATING THE SPUN FILAMENTS IN ACID SOLUTION, COLLECTING THE REGENERATED FILAMENTS IN THE FORM OF A CAKE, PURIFYING THE FILAMENTS IN CAKE FORM AND DRYING THE CAKE, THE IMPROVEMENT WHICH COMPRISES WASHING THE CAKE WITH AN AQUEOUS SOLUTION OF A LOWER ALIPHATIC ALDEHYDE PRIOR TO THE DRYING OF THE CAKE. 